Over the past three decades, there have been major advances in the data processing industry that have revolutionized the manner in which information is gathered, stored, interpreted and processed. One advance has been the expansion of technological sophistication, as exemplified by the microprocessor chip. That is, data processing power which once required rooms full of equipment and kilowatts of electrical power to operate, can now be found in small silicon microprocessor chips. Another advance has been the cost of purchasing such data processing power. In particular, in the area of memory, where costs have dropped and capacities have increased, there has been an inevitable rush to fill newly available memory space with information. In this respect, the demand for more memory and storage space has always seemed to surpass the available supply of such space.
For users with exceptionally large data storage needs, individual mass storage devices such as magnetic tape and disk drives have not been able to satisfy the need for more storage space. Traditionally, the need for more storage space in such storage devices has been addressed by merely adding additional magnetic tape drives and/or disk drives to form multi-component storage systems. This has proven costly both in terms of expense and floor space.
Significant strides have been made in recent years toward increasing the data storage capacity of individual mass storage and random access memory devices. Despite these technical advances, all known mass storage devices are restricted by limitations imposed by mechanically rotated or translated media.
For example, a limitation on "storage density" is imposed by mechanical and physical tolerances in known storage devices. For rotating disk and linear velocity magnetic tape storage systems, the tolerances associated with individual mechanical/physical components involved in media movement accumulate to limit the density of individual data marks on the media. Tolerance accumulation amounts to an estimated density loss of twenty-five percent in data storage capacity for "fixed media" rotating disk storage systems. This percentage increases for rotating disk storage systems utilizing "removable media" due to the compounding effect of the tolerances associated with the various media that can be mounted in such systems.
Manufacturers have developed methods to compensate for tolerances associated with moving (i.e. rotating or translating) media. While compensation methods vary from manufacturer to manufacturer, such methods typically result in reducing the "density" of data storage on an individual media. Examples include larger marks or domain areas on the media, larger gaps between individual data marks on a track, greater track separation, additional inserted error correction bits, and insertion of high resolution materials into the media to highlight individual domains.
As a consequence of rotating disk or linear velocity tape movement, operational control systems for controlling such movements must be imbedded into the device. Examples of these control systems include managed read/write speeds, enhanced servo positioning systems, shock and vibration control systems, and enhanced error correction schemes. As these control systems operate in conjunction with the reading and writing of data, they adversely impact the speed of data storage and retrieval.
Another limitation arises as a consequence of the apparatus and techniques used to record data on and read data from the media. This limitation impacts the rate at which data is recorded or the rate at which it is retrieved.
Each individual mark on the media must be accurately stored and read to ascertain the information represented by the mark. Historically, a central goal in the mass storage industry has been to reliably and repetitively store and/or retrieve data one bit at a time using a single head assembly. Typically, the stored data is retrieved from the media and transferred serially from a mass storage device to a requesting device over a single data channel.
An improvement to the single head assembly, which results in a substantially increased the rate of data retrieval, is a rotating disk system utilizing multiple heads set in a vertical comb. The heads are inserted between multiple disks stacked concentrically on a common spindle for reading or writing a bit from each disk. Bits read concurrently are located at a common track and bit position for each disk in the stack. This multiple head assembly requires, and is limited by, close mechanical tolerances. The data bits read by each head are fed into a channel in a sequential manner, but the group of channels is synchronized for each bit read to create an eight bit (i.e. one byte) parallel channel. Each byte of data is eventually converted to a serial format for delivery to a CPU. The one bit per side output from a single fixed stack mounted in a drive is the nominal maximum achievable by a rotating drive machine.
In both single head/serial data transfer and ganged head/parallel data transfer storage devices, the data rate is controlled by two mechanical restraints. The first is the speed that the media is moved past the head(s), and the second constraint is the speed and accuracy that a mechanical arm can be positioned and maintained over the data tracks for read and write operations. Other head configurations that have been developed, such as multiple heads and helical scanning, have the same two limitations (i.e. rotational or linear speed of the media and mechanical positioning of the head(s)). The optical industry's current efforts to increase rotational speed by several times to improve data rates only serves to validate these constraints.
These limitations on the data rates of recovery/storage in known storage devices have lead developers to time buffer the interface between the storage device and CPU with one or more solid state memory (RAM) devices. This buffering scheme is commonly referred to as a "cache memory" system. The RAM devices are usually as fast as the CPU. Although the RAMs normally do not parallel the size of a storage device, they are sufficiently large to accommodate the largest drive file and are capable of distributing data at a rate proportional to the highest rate transmitted/received by the CPU or the storage device.
Cache memory systems are necessary, but expensive, hardware especially in light of their increasing size within a computer system. RAM memory devices are on the order of two magnitudes more expensive than equivalent mechanical storage alternatives. Also cache memory systems require a uniquely independent hardware, architectural, and software structure compared to mechanical storage. This adds to the cost of a cache memory system in a mass storage system implementation.
The industry developed "Extended Memory System" is an attempt to reduce the cost of cache memory systems. Extended memory software systems expand the capability of RAM by utilizing preassigned fixed hard disk memory as RAM whenever the solid state RAM capability has been exceeded. This technique, however, is a software translation rather than a true physical integration of the memory devices. Recovery or storage of data within an extended memory space is accomplished at essentially the same rate as that of normal archival storage due to the use of serial buses and the mechanical restraints previously noted.
As the demand for larger storage devices, larger file structures, and faster retrieval/storage intervals increases, demands on caching are expected to increase. In parallel with these volume increases, larger and faster file transfers between archival storage and RAM will be required. Unless these two independent structures are integrated, the delays arising from transferring data between them are expected to increase.
In view of the foregoing, it is apparent that a new type of data storage system is needed. It is therefore a principle object of the present invention to provide a mass storage/memory system that features enhanced digital storage capacities, accelerated data rates, an integrated RAM and archival memory system, open format ports, and a multiplicity of internal read/write channels.